Earth rod

[gonch69]

Just noticed my earth rod is on its last core so need cutting and reconnecting dumb as it may sound do I need to turn off power
Thanks

 

[ericmark]

Yes safer if you do, but wonder how you noticed, the earth rod should be in an earth pit so no one can touch the rod or the ground around it, as under fault conditions it could be live.

Be aware GPO party line telephones needed an earth rod, these are no longer required, party lines went in the 70's, but the rods often remain with a un-insulated wire often clipped to outside of house, are you sure it is an earth for the electric supply?

 

[gonch69]

Thanks for quick reply were overhead power line
I notice the plastic cover was cracked I reason I looked

 

[sparkwright]

Just noticed my earth rod is on its last core so need cutting and reconnecting dumb as it may sound do I need to turn off power
Thanks

What does that mean, on its last core?

EDIT. Earth rod cable connected by only one strand, perhaps?

 

[ericmark]

The whole idea of this is to keep you a safe distance from the earth rod, once repairs are made one needs to test, this explains how the rub is it needs special testing gear, so not really a DIY job.

 

[JohnW2]

The whole idea of this View attachment 300362 is to keep you a safe distance from the earth rod,....

I think I need some education here. Under what circumstances is it necessary, or even desirable, to "keep a safe distance" from an earth rod - and, while we are at it, what is that "safe distance"?

Kind Regards, John

 

[ericmark]

I would also like to know safe distance, since an earth rod can be 60 Ω, a 3 kW heater connected to earth instead of neutral due to a fault, would raise the voltage at the earth rod to 177 volt, this would reduce as the distance to earth rod is increased, and although this was possible, today the use of RCD's means within 40 mS the supply is removed, so the danger is not there for long. Prolonged danger from an earth rod is only likely where it should have never been fitted as the supply is TN. However there was a move at one time to fit earth rods to TN supplies.

My parents old house I am sure had an earth when I was a boy, as I managed to blow a 13 amp fuse due to an earth fault, but around 2004 when I came to work on the electrics I found no earth, the only earth rod found was for the old GPO party line, how it originally got its earth or how it was lost, no idea, but the fact is unless tested you can go for years without an earth and be unaware it has gone. Bonding was still there, but no sign of an earth.

So I would say when working on an earth rod rubber gloves are order of the day, and after working on it, if there is power then comparing it to DNO earth with a loop impedance tester is the easy option, other wise one needs a garden large enough to lay out the test probes, the distance from the earth rod will depend how deep it goes, most domestic 60 Ω is good enough, but where I worked looking for 8 Ω and that needed between 2 and 6 1.2 meter rods.

They teased me I had been given the job as I had zero potential. I spend 6 months fitting earth rods on a gas terminus at Point of Aye.

 

[gonch69]

Yes one strand was what I ment the cover was just one of these

 

[ericmark]

I would turn off supply before fixing and wear gloves, but likely even if you don't you will not get a shock.

 

[Taylortwocities]

I would turn off supply before fixing and wear gloves, but likely even if you don't you will not get a shock.

Unless an earth fault occurs in the installation at the time. If that happens the earth wire will be at 230volts. This could be fatal to the OP.

@gonch69 turn off the main switch before carrying out the repair.

 

[gonch69]

Thanks all

 

[JohnW2]

I would also like to know safe distance, since an earth rod can be 60 Ω, a 3 kW heater connected to earth instead of neutral due to a fault, would raise the voltage at the earth rod to 177 volt, this would reduce as the distance to earth rod is increased, ...

The actual load is irrelevant. One needs to consider the 'worst case' scenario, which would be a low-impedance L-E fault, leading to the potential of the earth rod (above 'true earth') rising to virtually supply potential (230 V or whatever).

However, I'm not sure of what sort of 'risk scenario' you are envisaging, since what you say sounds rather 'back to front' ....

...the potential of the 'ground' (soil etc') in the immediate vicinity of the earth rod should be very similar to the potential of the rod. Hence someone in contact with the rod and the immediately surrounding ground/soil should experience only a minimal pd. The further one gets from the rod the closer will potential of the ground/soil get to true earth potential, so the pd they will experience should increase with increasing distance between contact with the rod and contact with the soil (i.e. the opposite of what you seem to be suggesting), shouldn't it?

Kind Regards, John

 

[ericmark]

It seems the gradent is in a logarithmic progression, and the distance will also affect the effect, seems 25 volt is enough to kill a cow, back in the 70's when traffic senced portable traffic lights came out, Forest City Electrics had to recall loads of traffic lights due to the Mulard microwave detectors using the earth as a return, so could make the heads 55 volt to earth under fault conditions.

There have been cases of dog deaths due to pavement voltage, few other animals would be forced to walk over the fault, but dogs on leads have little option but follow their owner.

Using 4 legs worse than 2, and shoes clearly help, and the larger the stride the worse, but as yet not seen any figures as to at what distance the gradent is safe.

 

[JohnW2]

It seems the gradent is in a logarithmic progression,

I think that's roughly true - but it's the direction of the gradient I'm talking about ....

.... the greater the distance one is from an earth rod which has become 'live', the closer will be the the local potential to that of true earth, hence the greater the pd between the rod at that point - which seems difficult to reconcile with the "keeping a safe distance" from the earth rod that you spoke of.

and the distance will also affect the effect,

The gradient' is a gradient over distance. What point are you trying to make?

seems 25 volt is enough to kill a cow,

I'm not sure of the voltages for different species, but large 4-legged animals are obviously at greater risk, since they have the ability to have quite large distances between points of contact with the ground, which can be an issue if there is a very large voltage gradient.

Using 4 legs worse than 2, and shoes clearly help, and the larger the stride the worse, but as yet not seen any figures as to at what distance the gradent is safe.

I don't think you'll ever find a general answer to that question, because 'it depends' on so many factors in an individual case.

Kind Regards, John